1. Field of the Invention
The present invention relates to a sheet feed table for feeding a sheet fed onto a feeder board by sheet feed rollers of a sheet feeder of a sheet press while registering the sheet in a lateral direction or a direction perpendicular to a sheet conveyance direction between the feeder board and a feed board.
2. Description of the Prior Art
A plurality of conveyance tapes, extended on a feeder board, for conveying a sheet, a feed board for slidably feeding the conveyed sheet, a registering device, arranged at the distal end portion of the feed board, for registering a sheet in the sheet conveyance direction, and a swing device for feeding the registered sheet to printing units are arranged between a sheet feeder and the printing units of a sheet rotary press. The feeder board and the feed board are coupled through a conveyance table, a so-called "ditch board", and side lay devices for registering the sheet in the lateral direction are arranged at two sides of the conveyance table.
When a sheet size is changed, the total width of the conveyance table must be increased or reduced accordingly and the positions of the side lay devices must be adjusted. Conventionally, the conveyance table is divided into several sections in the widthwise direction of the sheet, so that a central one is fixed and several ones at two sides thereof are detachably mounted. Each time the sheet size is changed, a required number of sections of the conveyance table are mounted or removed and the positions of the side lay devices are adjusted in accordance with the sheet size.
However, in the conventional detachable structure of the conveyance table, a plurality of pairs of front and rear leaf springs are arranged on the back side of conveyance boards to be perpendicular thereto, and a stay, extending below the conveyance boards, for supporting the side lay devices is clamped by these leaf springs in the back-and-forth directions. Therefore, this structure poses various problems.
More specifically, if the biasing force of these leaf springs is weak, the leaf springs rattle during the operation of the press, resulting in noisy operation. In addition, print trouble often occurs due to vibration. If the biasing force of the leaf springs is strengthened in order to prevent this, it becomes difficult to remove the conveyance boards. If the conveyance boards are forcibly removed, the leaf springs may be damaged. Upon repetitive mounting/removing operations, the biasing force of the springs is attenuated.
The present applicant has proposed a sheet conveyance table which is free from the above drawbacks, as described in Japanese Utility Model Prepublication No. 57-155375. This conveyance table will be described below with reference to FIGS. 4 and 5. FIG. 4 is a schematic side view partially showing a multicolor sheet rotary press which includes this sheet conveyance table, and FIG. 5 is a perspective view of the sheet conveyance table. The rotary press is composed of a sheet feeder 1 and a plurality of printing units 2 (only one unit is shown). The sheet feeder 1 includes a sheet stacker 4 which stacks sheets 3 thereon and moves upward as the number of sheets 3 decreases upon sheet feeding, and a sucker device (not shown) for drawing the sheets 3 by suction one by one from the uppermost sheet to feed them between a pair of sheet feed rollers 5 and 6. Each printing unit 2 has a plate cylinder 7 on the peripheral surface of which a print plate is mounted, a rubber blanket cylinder 8 to which an image formed on the plate surface is transferred, and an impression cylinder 9 for applying a printing pressure to the sheet 3 passing between itself and the rubber blanket cylinder 8. A transfer cylinder 10 for transferring the sheet 3 is arranged between the impression cylinders 9 of adjacent printing units 2.
A feeder board 11 is arranged between the sheet feed rollers 5 and 6 and the front edge portion of the printing unit 2 to be slightly inclined. The feeder board 11 is formed of a wood plate and has a width slightly larger than the maximum width of a sheet. A pair of rollers 12 and 13 are axially and rotatably supported near the front and rear edge portions of the feeder board 11. A plurality of conveyance tapes 14 are arranged between the rollers 12 and 13 to be parallel to each other in the widthwise direction of the feeder board 11, and their upper traveling portions are in contact with the feeder board 11. Reference numeral 15 denotes a small frame for supporting the rollers 12 and 13 and the feeder board 11. The small frame 15 is rotatably fixed to the frame of the sheet feeder 1 by a bracket (not shown) and is capable of moving upward with the roller 12 as the rotatable edge. The rotatable edge side member is supported by a hook-shaped member provided on the frame side of the printing unit 2. In front of the small frame 15, a feed board 16 having substantially the same width as that of the feeder board 11 is arranged between the frames of the printing unit 2 to form a predetermined gap between itself and the front edge of the small frame 15 and to be inclined through substantially the same angle as that of the feeder board 11. A registering device having a front lay 17 or the like is arranged on the front edge portion of the feed board 16. Reference numeral 18 denotes a swing device which grips and swings the sheet 3 which abuts against the front lay 17 and is stopped, to cause the grippers of the impression cylinder 9 to alternately grip the sheet 3. Although not shown, a sheet urging roller for urging the sheet 3 against the conveyance tapes 14 is arranged above the feeder board 11.
A stay 19 is supported between the small frame 15 and the feed board 16, such that its two ends are fixed to right and left frames 20 of the printing unit 2. Known side lay devices 21 for registering the conveyed sheet 3 in the lateral direction are mounted on the two end portions of the stay 19 to be movable in the widthwise direction of the press for adjustment. A central conveyance board 23 constituting a conveyance table together with the stay 19 and a plurality of conveyance boards 24 are arranged on the stay 19 to be parallel to each other in the widthwise direction of the sheet 3. The central conveyance board 23 has a width slightly larger than a prospective minimum width of a sheet, and is fixed to the stay 19 by screws. The number of the conveyance boards 24 is selected in accordance with the size of the sheet 3, and they are mounted on or removed from the stay 19. Although not shown, the conveyance boards 24 are mounted on the stay 19 to be attracted by rubber magnets buried in the stay 19 so as not to be movable. When metal members arranged on the back surfaces of the conveyance boards 24 abut against the stay 19 and the front edges of the conveyance boards 24 are engaged with the stepped portion of the feed board 16, their movement in the back-and-forth direction is restricted.
With the above arrangement, the sheets 3 stacked on the sheet stacker 4 are drawn by suction one by one by the sucker device and are fed forward. The sheet 3 is then caught by the vertically aligned sheet feed rollers 5 and 6 to be fed onto the conveyance tapes 14, and is conveyed thereby. The conveyed sheet 3 is released from the conveyance tapes 14 at the position of the roller 12, and is fed onto the conveyance boards 23 and 24. Then the sheet 3 slides along the conveyance boards 23 and 24, and along the feed board 16 until it abuts against the front lay 17 to be registered in the sheet conveyance direction. Then the sheet 3, which is at a stand still with one edge thereof held in contact with the front lay 17, is pulled laterally to be registered in the lateral direction. Then the sheet 3 is gripped by the swing device 18, and is then gripped by the grippers of the impression cylinder 9 to be subjected to printing while being conveyed.
Assuming that the sheet size is changed from the maximum size to one having a smaller width, the conveyance boards 24 is removed from each end, and the side lay devices 21 are moved a predetermined distance toward the center. In this manner, as the size of the sheet 3 is reduced, the outside conveyance boards 24 are removed one by one, and only the fixed conveyance board 23 is used for a minimum sized sheet.
In the conventional sheet conveyance table, since the conveyance boards 24 are attached by the rubber magnets, no noise is generated and they can be easily mounted or removed. However, since the conveyance boards 24 must be removed or added each time the sheet size is changed, this results in a cumbersome operation and takes much labor and time. In addition, since a portion under the conveyed sheet 3 is entirely shielded by the conveyance boards 23 and 24, an airflow interposed between the sheet 3 and the conveyance boards 23 and 24 cannot escape, so that the sheet 3 swells, resulting in misregistration.